This Program Project, Neurolinguistics and Biologic Mechanisms in Dyslexia, represents a natural extension of our efforts to develop a classification of reading and learning disability. Such an enterprise encompasses and yet gets to the heart of some of the most central issues in reading disability research including definition, mechanisms, and strategies for intervention. In this renewal, we propose to investigate the developmental course of the topologies of reading and learning disability. More specifically, we hope to clarify the nature of the cognitive and neurolinguistics deficits underlying reading disability in young children and in older children, the relationship of these deficits young children and in older children, the relationship of these deficits to one another and to the reading process and their course over time. The Program Project encompasses four projects and two cores. Project I addresses: 1) temporal stability of subgroups of learning disability (LD) and subtypes of reading disability (RD); 2) nature and determinants of outcome of specific subgroups of LD and subtypes of RD; 3) nature and determinants of plateau effects; and 4) cognitive and neurolinguistics mechanisms influencing RD. Project II is designed to study the growth and development of reading related language skills (e.g., phonological awareness) in children with language disorders; an additional goal is to explicitly examine the influence of social disadvantage on language and reading disability. Project III adds a new dimension to our studies by examining the endocrinologic influences on the rate of development of academic and cognitive skills. Project IV extends our previous neuroimaging project which developed rigorous methodologies to examine particular brain structures between well described subject groups. The elucidation of the mechanisms and the subtypes of reading disability are intimately related and serve as a necessary prerequisite to informing strategies for designing practical intervention measures for prevention and treatment.